1. Field of the Invention
The present invention is directed to an apparatus for correlating geometric information regarding an examination subject, which are acquired in a tomographic imaging device, to measuring points which are acquired from the same examination subject in a different measuring apparatus, such as a biomagnetic measuring apparatus.
2. Description of the Prior Art
The measurement of biomagnetic signals is becoming an increasingly utilized medical diagnostic tool as described, for example, in the periodical "Bild der Wissenschaft," No. 8, 1986, pages 76-83. Extremely weak biomagnetic signals can be acquired by so-called SQUID systems. Those signals include, for example, so-called evoked magnetic fields of the human brain, which are on an order of magnitude of only 10.sup.-14 T. For undertaking such a measurement, the test subject is brought into a magnetically shielded measuring room, and the patient's head is scanned in a non-contacting fashion with the SQUID system or a magnetometer. The data acquired in this manner are evaluated by a computer based on a pre-determined mathematical model. Further patient data are required, particularly data identifying the geometry of the patient, for example, identifying the structure, size and extent of the brain. The further patient data can be obtained using different examination techniques, such as ultrasound, computer tomography, or magnetic resonance imaging. It is a problem in the art to coordinate the biomagnetic test results with the results of the other imaging methods. The problem of coordination of the different signals can be further explained with reference to the example of a magneto encephalogram measurement (MEG), and a nuclear magnetic resonance tomograph image. Coordinating the data from these two measurement systems requires (a) identification of the position and orientation of the head of the patient relative to the detector array in the MEG measurement, (b) fixing the head during the MEG measurement, and (c) identification of the position and orientation of the head in the MR image relative to the position and orientation of the head in the MEG measurement, or vise versa.
Only when the above problems have been satisfactorily, resolved can a point in the MR image be unambiguously coordinated to each of the measuring points of the head identified with the SQUID gradiometer. Stated in more general terms, the problem is to determine what geometrical relationship exists between the individual measuring points of the MEG measurement and the contour of the brain which is identified in a tomography imaging method, and is represented in a tomogram. Another statement of the problem is to determine the geometrical coordination of information regarding an examination subject which were acquired in a tomographic imaging apparatus relative to the measuring points which were acquired from the same examination subject in a measuring system for biomagnetic signals.